It is known to provide fork-lift trucks with a chassis having wheels which can be driven directly or indirectly from an internal-combustion engine and provided at one end of the chassis, in the direction of displacement thereof, with a mast upon which a fork is vertically displaceable. At the other end of the chassis, a counterweight is provided to balance the load which may be lifted by the fork, thereby preventing tipping of the chassis of the vehicle about the front wheels thereof.
When an internal-combustion engine constitutes the prime mover of the vehicle, it may be used to drive a hydrostatic transmission, i.e. the axial-piston pump of a hydrostatic transmission whose hydrostatic motor or motors is or are connected to the propelling wheels of the vehicle.
The internal-combustion engine is a substantial source of noise and vibration and it is known that the acoustic output of the engine radiates from practically all of its external surfaces.
However, it has been found that substantial noise is also emitted through the intake passages of the engine.
With air-cooled internal-combustion engines, the cooling blower or fan constitutes an additional noise source and noise is also produced by the ribbed cylinders and the cylinder head. Not only does noise of the internal working of the engine radiate from these surfaces, but the passage of air over the ribbed cylinders and cylinder head produces additional noise. Thus the air-cooling passages of the engine constitute a significant contributor to the noise output of this machine.
In water-cooled internal-combustion engines, the noise is emitted from the surfaces of the engine and from the fan which draws air through the radiator serving to cool the liquid circulated within the engine.
As a consequence, an internal-combustion engine when used in a fork-lift truck constitutes a substantial noise source. This noise is in addition to the noise generated by the propelling transmission, i.e. the hydrostatic pump mentioned previously for propelling the vehicle as well as the pumps provided for auxiliary functions including lifting the fork, power steering and the like.
In conventional fork-lift trucks, the internal-combustion engine and the remaining drive elements mentioned previously can be provided in a free space, hereinafter referred to as the engine compartment, which can be open into a warehouse or other building in which the vehicle may be used. In general, the noise-damping effects of conventional means for reducing the output of the engine compartment used heretofore have been of limited success.
For example, in LINDE fork-lift trucks, attempts have been made heretofore to minimize the noise output but even in these systems straight passages are provided through the counterweight for drawing the cooling air into the system or blowing the cooling air out of the latter. However, the engine compartment is provided with a synthetic-resin hood which emits significantly less sound than sheet-metal hoods which have been used widely heretofore. The interior of the engine compartment and the inner surfaces of the hood can be provided with layers of acoustic damping. Nevertheless the drive systems for such fork-lift trucks have been known to have extremely high noise outputs which have rendered them disadvantageous and frequently unusable in certain locations or in many applications.